The study will assess the effect of amalgam on antibiotic resistance in bacteria. University of Washington will collect and assay oral and urine samples from 150 participants in the University of Washington/Casa Pia Trial (UWCPT) and will collect and analyze quantitative data from these samples. Specific aims of this study are to determine if there are changes in the prevalence of antibiotic resistant and mercury resistant oral bacteria in children 8-10 years who are treated for dental caries with dental amalgam and those treated with composite filling material between baseline (pre- exposure) to 3 months (immediate post-exposure) to 12 months; to determine if there are differences in changes in the prevalence of antibiotic resistant and mercury resistant oral bacteria for the two groups of participants; to determine if there are changes in the prevalence of antibiotic resistant and mercury resistant enteric flora in the two groups between pre-exposure and the three post-exposure endpoints; to determine if there are any differences in changes in the prevalence of antibiotic resistant and mercury resistant enteric flora for the two groups of participants; and to determine if there is a linkage between the acquisition of mercury resistance and the acquisition of antibiotic resistance genes in oral bacteria and, separately, in enteric bacteria.